It has recently occurred to me that the running theme throughout Mass Effect 3 is the idea of unification between two intractable enemies -- and the mutual redemption of both -- triggered by the martyrdom of a major character. It's hard to get this concept, depending on some of the choices you made, but the "unification" scenarios seem to be:

Tuchanka:
Mordin sacrifices himself to cure the Genophage, which allows Eve to lead the Krogan out of their barbaric rut and rejoin the intergalactic community with the Salarians and the Turians (Eve doesn't count as a sacrifice because 1) she's not a major character and 2) her sacrifice means nothing if MORDIN doesn't put his ass on the line to spread the cure).
This is also echoed by Lieutenant Victus doing the bomb jump, killing himself in the process of saving a Krogan city and preventing a war between the Krogan and the Turians.

Rannoch:
If you do things right, Legion winds up sacrificing himself to reunite the Quarians and the Geth, resulting in the Geth achieving sentience and the Quarians getting their planet back.

The conflict between the Geth and the Quarians was centuries old, and the Genophage had plagued the Krogan for over a millennia. Compared to those two conflicts, the war against the Reapers is just a flash-in-the-pan, but it is still resolved the same way: the war's greatest hero makes a sacrifice and -- somehow -- unites the two warring factions (e.g. the Synthesis/Control endings).

This being mass effect, you also have the option to AVOID reunification and completely screw over one faction or the other; thus, on Tuchanka you can go ahead and cure the genophage even without Eve (or better yet, Wrex) being there to keep the Krogan in line; under Wreav's leadership, the resurgent Krogan are pretty much gauranteed to tear the Salarians a new asshole once the reapers are dealt with. On the flip side, you can screw the Krogans by giving them a fake cure and dooming them to eventual extinction.

On Rannoch it's even simpler: you can throw the Geth under a bus to gain the Quarians as allies, or you can screw the Quarians and take the Geth home with you (or you can do BOTH, take the Geth as allies and then nuke them with the Destroy ending).

Point is, I think it went over everyone's head -- even mine, until recently -- that what we're really being presented with is the same choice we had two other times in Mass Effect 3: to either obliterate one of the warring factions to the temporary benefit of the other, or you UNITE those two warring factions for a longer-lasting peace. The fact that one of those warring factions happens to be your OWN slightly obscures this; with Synthesis or Control, Shepard is making the same choice Mordin made if/when he sacrificed himself for the cure, or that Legion made if/when he uploaded himself to the Geth Consensus. The idea of peaceful coexistence with the Reapers only seems crazy because the Reapers are omnicidal assholes who've never expressed any desire for peace, but from various perspectives this is equally true of the Krogan AND the Quarians, and reconciliation is possible in both cases.